Conventional semiconductor device fabrication is generally based on growth of lattice-matched layers. A lattice mismatched epitaxial layer at a semiconductor interface can lead to a high density of dislocations that degrade semiconductor device performance. Over the past several years, however, there has been increased interest in epitaxial growth of lattice-mismatched semiconducting material systems. Lattice mismatched systems can provide a greater range of materials characteristics than silicon. For example, the mechanical stress in a lattice mismatched layer and control of its crystal symmetry can be used to modify the energy-band structure to optimize performance of optoelectronic devices. Lattice mismatched systems can also enable compound semiconductor devices to be integrated directly with Si-based complementary metal oxide semiconductor (CMOS) devices. This capability to form multifunction chips will be important to the development of future optical and electronic devices.
Problems arise, however, because an epitaxial layer of a lattice-mismatched material on a substrate is often limited to a critical thickness (hc), before misfit dislocations begin to form in the epitaxial material. For example, hc=2 nm for a germanium epitaxial layer on a silicon substrate. Because of the relatively small hc and the large dislocation densities at thicknesses greater than hc, use of the heteroepitaxial layer is impractical.
Thus, there is a need to overcome these and other problems of the prior art and to provide a method to grow defect free heteroepitaxial layers of lattice mismatched systems.